1. Field of the Invention
The present invention relates to an apparatus and method for supporting a handover in a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for supporting a handover from a macro Base Station (BS) to a micro BS.
2. Description of the Related Art
In general, voice services have been a primary concern in the development of communication systems. As communication technologies have advanced, various multimedia and data services, in addition to the voice services, are becoming increasingly important. However, voice-based communication systems have failed to satisfy user demand for multimedia and data services due to a relatively small transmission bandwidth and expensive service fees. Moreover, growing demand for Internet services has resulted in an increased need for a communication system capable of effectively providing the Internet services. To cope with such user demand, a broadband wireless communication system has been introduced to effectively provide broadband Internet services.
In addition to voice services, a broadband wireless communication system supports various data services with a high or low speed as well as multimedia application services (e.g., high-quality video). That is, a broadband wireless communication system can access a Public Switched Telephone Network (PSTN), a Public Switched Data Network (PSDN), an Internet network, an International Mobile Telecommunication (IMT) 2000 network, and an Asynchronous Transfer Mode (ATM) network in a fixed or mobile environment based on a wireless medium using a broadband spectrum (e.g., 2 GHz, 5 GHz, 26 GHz, 60 GHz, etc.). Furthermore, a broadband wireless communication system can support a channel transmission rate of 2 Mbps or more. A wireless communication method of a broadband wireless communication system is being standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 group.
At present, in a broadband wireless communication system, installation of a micro Base Station (BS) is being considered. The installation of a micro base station is provided to complement a macro BS. More specifically, the micro BS is a home BS or a Small Office Home Office (SOHO) BS, which is installed in an area that is not covered by a service area of the conventional BS or in an area where service quality is unsatisfactory due to weak signal strength. Similar to the macro BS, the micro BS provides a portable Internet service to a Mobile Station (MS). The micro BS can be characterized by low output, small capacity, and low cost, which are optimized for a small indoor environment (i.e., home or SOHO). Two important aspects of the micro BS are that it must be able to interoperate with the macro BS, and a conventional MS must be able to receive a service while switching between the micro BS and the macro BS. More specifically, improved quality services must be provided without interruption to the MS by performing a handover between the macro BS and the micro BS according to a wireless environment.
In a conventional handover process, when a handover request is made to a neighbor cell or a neighbor sector according to changes in a user's communication environment, an MS measures a channel condition of neighbor BSs on the basis of downlink signals received from the neighbor BSs. For example, in a broadband wireless communication system, a serving BS receives information on the neighbor BSs from a BS management server and broadcasts a MOBile_NeighBoR_ADVertisement (MOB_NBR_ADV) message including the information about the neighbor BSs. In this case, the MS performs a series of scanning operations for measuring the channel conditions of the neighbor BSs on the basis of the MOB_NBR_ADV message.
To perform the conventional handover process using a handover between a serving macro BS and a target micro BS, specific information about the target micro BS must be included in the information transmitted by the BS management server to the serving macro BS. However, at present, the BS management server does not manage the information on the target micro BS. Thus it is not possible to transmit the information on the target micro BS through the MOB_NBR_ADV message. That is, a handover from the macro BS to the micro BS cannot be achieved using the existing IEEE 802.16e technique.
Accordingly, there is a need for a new method for supporting a handover from the macro BS to the micro BS in a broadband wireless communication system.